This invention relates to computed tomographic (CT) imaging, and more particularly to methods and apparatus for weighting projection data acquired using a multi-slice CT imaging system.
For some known multi-slice helical scans, reconstructed with a fan-beam based algorithm, there is an error due to a cone beam effect of a projection sampling. The error in a reconstructed image increases with an increase of a distance of an image pixel to a system iso-center. Therefore, for pixels located near the system iso-center, a plurality of projection rays are near a reconstructed pixel location and an amount of cone beam error is relatively small. For pixels that are located further away from the system iso-center, a difference between the location where the projection sample passes and the location of the backprojected pixel is large and the amount of cone-beam error is relatively large.
In one aspect, a method for weighting projection data is provided. The method includes selecting a region that includes a plurality of projection data samples, dividing the region into a plurality of equally sized sub-regions, and weighting the equally sized sub-regions using a location dependent z-smoothing weighting function.
In another aspect, a computer for weighting projection data acquired using a medical imaging system is provided. The imaging system includes a radiation source and a detector. The computer is programmed to select a region that includes a plurality of projection data samples, divide the region into a plurality of equally sized sub-regions, and weight the equally sized sub-regions using a location dependent z-smoothing weighting function.
In a further aspect, a computed tomographic (CT) imaging system for weighting projection data is provided. The CT system includes a radiation source, a detector array, and a computer coupled to the detector array and the radiation source and configured to select a region that includes a plurality of projection data samples, divide the region into a plurality of equally sized sub-regions, and weight the equally sized sub-regions using a location dependent z-smoothing weighting function.